Pilot wire control for automatic reclosing circuit breakers



Jan- 1, 1952 w. L. sPRl-:NGLE

PILOT WIRE CONTROL FOR AUTOMTIC RECLOSING CIRCUIT BREAKERS Filed June27, 1946 IN V EN TOR. //uM/r/ l Spee/vaas Patented Jan. l, 1952 PILOTWIRE CONTROL FR AAUTOMATIC RECLOSINGLCIRCUIT'BREAKERS Wiuiam L.sprengie, Pittsburgh, Pa., assigner to IFT-,E Circuit'Breaker Company,Philadelphia, Pa., av corporation'olfA Pennsylvania Application June2.7, 1946, serial No. 679,597y

1 Claim, (ci. 1754294) My invention relates to electric power systems;v

and'more particularlyrelates to control of power circuitsin mines.

Inthe Voperation of power circuits.in .minesp` automatic reclosingcircuit breakers areemployed for the protection of thepower lines.,AilVV hazard, however, is created when for any vreason the ,overheadtrolley which carries electric power breaks ,due, for example, to afalling roof.. In

such cases reclosing of the circuit breaker ref creates the shortcircuit which may initiate-lires of-a serious nature.V

In suchcases, it is desirable that the automatic reclosingrcircuitbreakenshall not reclose as it normally would when tripped inv responseVto a. shortv circuit`V or other. circuit,fault'conditions.l Areclosing`4 of the circuit breaker whenr a ,me-Y, chanical failure suchas a fallingeroof occurs mat?` result inserious fires.4

, Inaccordance with mypresent invention I which. ,determines whether;the breaker will. yre-V close after beingtripped open. If the mine rooffalls, the pilot wire breaksdand completes cir-I cuits withthe f trolleysuch that theY automatic l circuity .l breakers controllingA power fed'vto the trolley is opened and held opened until. repairs cllli4 breaker,automatically closesv without lrequir-Y much as the circuit breaker islocated atar con.--

siderable. distance from wherel the break may occur.I

Accordingly, anobj ect .of my invention is t0, provide novelciruitrrangemtnt fin 00.11116@ tion.` with automatic reclosingvcircuitbreakers which in response tofaultyconditions has opened and staysopened until the Yfault is repaired..

Alvfurther object of my invention is to provide novel circuitarrangements whereby an automatically reclosing circuit breaker isautomatically closed ,when the fault isrepaired.Y

`Still another object of vmy invention is to provide novel loadmeasuring conditions for controlling the reclosing of an automatic'circuit breaker.

These `and other objectsof, my invention Awill bevr more fullyvunderstood in connection with the attached drawing, which isl a Yschematic circuit diagram of myinvention.

Normally, powerV is supplied-from the power line l, through theclosed.contacts of thecir: cuit breaker 2, through the overcurrent relay 3, tothe trolley 4,' which feeds energy through the load'l'to the negativereturn which maybe a railv 6.l I f a fault occurs,`'cir :ui`tY breaker 2is automatically tripped open in'responsefto the overload currents whichwill iiow through the overcurrnt relay 3, inv a mannerwhich iswell knownin the art.

lil

`open position due to a fault, a circuit'extends4 from power line l totrolley 4, which shunts 'the' This circuit" includes the two fuses 'iand S r(which 'inv the.' present illustration are 10 ampere fuses);`andl` "connected in series with these fuses are contacts' @and yI and,therload .measuring resistance l`2`.'fl Contactsl s `.and Il arecontrolr switchesv which? may be manually operated butlarefnormallylin.20 hayexprovided a, pilotwire, the; condition of Normally, the-circuitbreaker will aftera short interval of time, test the condition ofthecirl cuit and will reclose.

In the present invention itis desired that such reclosing, of thebreaker be prevented in the' event that the fault has been due to afallingj roof, which as stated above creates a 'condition which maybecome a re hazard unless'plwerA is immediately cut oi.

Assuming now that the circuit breaker 2 is in contacts ofV thecircuitbreaker 2.

closed position.

When, therefore, the circuit `breaker 2;openns., current from the vpowerline is 4still fe'jdov'er thisj by-pass circuit.y Uponv the openingofthe circuit breaker, therefore;n current is supplied to the trolley d,over the abo-renamed bypa`ss This, circuit extends tothe pilot wire I4,overv conductor425`, through fuse i5, through contact 2`--l,v thewinding of'relay I?, and to the negativere'-A turn (i.v

It will be noted thatthis circuit by-pas'ses' the resistory i8V which isof such size asto cause a" considerable voltage drop, therein so. as topre-j When, however, the by-pass circuit `is, complete on the closing4of i contacts 2,-l, the relay winding. Il is directly .connected acrosstheload 5..and measures the vcltageof this, load. Currentthrough thewind?" ing Il is suiicient depending on the loadcongvent operation ofthe relay.

ditionto operate its armatures.

UponA energization of therelay vI'l, to eiectV operation of itsarmatures to their closed poste Y tion, an energizingcircuit iscompleted froinfthe' power line l through Contact 9, through'nor'nally'Y closed contacts 3f-l and 3-2,con tro1led bythe` overcurrent relay3(nowde-V-energized), through lthecontacts y|'i-.-i and l'i.-2 ofrelayl'l (which isV now energized and therefore Yhas'operated ,itsarmatures to their' front engaging positions)-` throughY contactV 2 2;(which as in jthecase of contact 2-l is controlled to its closedpositionwhen'the circuit breaker isopened) and through the winding of the'relay2l tothe negative-re-l turn circuit 6;' Relay 21 is the'closingcontrolrelay and when energized. controls thecircuit for' the'reclosingmagnet.-

Upon energization of closing control relay 2|,

Contact 2-I inthe above described; circuit is mechanically connected tothe circuit breaker insuch a manner that it is operirwhen,V the circuitbreaker is closed and is closed ashortl intervalof time after thecircuit breaker opens..

its contacts 2I-I and 2I-2 are closed, by-passing the resistor 22 andcompleting an energizing circuit for the circuit breaker reclosingmagnet 23. The circuit breaker 2 is therefore reclcsed.

On reclosing of the circuit breaker, contacts 2-I and 2--2 are opened.Opening of contact 2-I has no effect on relay I1 since this relay findsan energizing circuit through resistance I8. Although as heretoforeexplained the current in this latter circuit is insufficient to pull upthe armatures of relay I'I, it is sufficient to maintain the armature inoperative position. Opening of contact 2-2, however, effectsde-energization of relay 2 I.

In the above operations which occur when the circuit breaker opens forany reason other than a failure of the roof, it will be noted that relayII, which is the load measuring resistance and which, it will be noted,is connected across the load when the circuit breaker opens, isdependent for its energization on current flowing through the pilot wireI4.

It will now be assumed that the circuit breaker is opened by a shortcircuit caused by a falling roof. The pilot wire I4 breaks as indicatedat the dotted line. The pilot Wire is an insulated solid copper wirewhich in practice is stretched between insulators one mile long or less,and is electrically connected to the trolley wire at 25. The trolleywire 4 and the pilot wire are suspended by insulators 26 and 2l from aroof 28 as in the case of a coal mine. In normal operations, a failureof the trolley circuit does not effect the pilot wire I 4 as describedabove. When, however, the roof falls the pilot Wire breaks at the timethe short circuit occurs and the operations now about to be describedoccur.

When the pilot Wire breaks, as for example, due to a falling roof, theconnection between the trolley and the pilot wire is broken. There is,therefore, no energizing circuit for the load measuring relay closingcoils I'I. This relay,`it will be recalled, was energized and remainedenergized on the first opening of the circuit breaker.

When now the break in the pilot Wire occurs as described above and thecircuit breaker is tripped because'of a short circuit, of trolley wireI4, the energizing circuit for the winding I'I is opened, and this relaydeenergizes if it had previouslybeen energized or it stays deenergizedwhen the circuit breaker opened, if not previously deenergized.

The deenergized condition to the winding I1 leaves the contacts I'I-Iand II--2 opened, so that although contacts 2-2 closes there is noenergizing circuit for the closing control relay 2l and this relaytherefore is deenergized. Moreover, the opening ofthe contacts I1-I andII--2 also opens the energizing circuit for the circuit breaker closingcoil 23. Accordingly, the circuit breaker is tripped and stays trippedpreventing powerfrom being fed to the trolley 4 except through the loadmeasuring resistor I 2.

When the pilot wire is repaired there is immediately supplied to theload `measuring relay closing coil I'I, sulcient current to energizethis winding. Therefore, reclosing of the circuit breaker is effected inthe manner described in detail above.

The operations above described may be summarized as the followingsequence of operations:

1. With the circuit breaker 2 in the open position, the control switches9 and I I are closed.

2. This by-pa-sses a load-measuring current around the circuit breaker2, through the load measuring resistor I2, through the load, and back tothe negative return.

3. The closing of the time delay closing contacts 2-I places the loadmeasuring relay closing coils, I'I, across the load voltage. If thepilot ywire is broken due to a roof fall, relay I1 will not pick up. Ifthe pilot wire is intact, the load measuring relay closing coils I1 arein proper relation for measuring the resistance of the load circuit.

4. If the load conditions are satisfactory, the load measuring relaycontacts I'I-I, I'I--2 close and energize the closing 4control relay 2l,which picks up and short circuits the resistor 22 causing the circuitbreaker 2 to close.

5. The closing of the circuit breaker 2, opens the time delay contacts2--I which de-energizes the closing control relay 2I and places theresistor I8 in series with the load measuring relay closing coils I1 andthe pilot wire.

6. If the pilot wire breaks, these coils are deenergized and the loadmeasuring relay contacts I'l-I, I'I--2 open, thus opening the circuitbreaker 2.

I claim:

In an electrical protective system having a circuit extending from asource of power to a load and including a trolley line and a returnline, a pilot wire extending adjacent to and parallel to said trolleyline and connected to said trolley line at its terminus,a circuitbreaker connected in said circuit, an overload relay connected in saidcircuit and responsive to a fault at said load for opening said circuitbreaker, a relay connectible in series with said pilot wire, a resistorconnected across said circuit breaker for providing a circuit from saidsource to said load when said circuit breaker is opened, meansresponsive to the opening of said circuit breaker for connecting saidrelay and pilot wire in series across said load and from said trolleyline to said return line for measuring the fault current produced bysaid fault at said load, circuit connections from said source of powerand including said resistor, pilot wire, relay and return circuit forenergizing said relay in the event the fault at said load has beencleared, said pilot Wire preventing completion of said circuitconnection in the event said pilot Wire is broken, a closing magnet forclosing said circuit breaker, yand circuit connections including saidclosing magnet controlled by said relay on energization thereof foroperating said closing magnet to close saidcircuit breaker.

- WILLIAM L. SPRENGLE.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS 14,463 Y, d GreatBritain Juiyfs, 179,63

